Mirror



Oct. 27, 1936. H, w, EDWARDS 2,058,429

MIRROR Filed June 19, 1955 fiverzr.

Patented Oct. 27, I 1936 v UNITED STATES PATENT OFFICE MIRROR and L. H. McGowan Application June 19, 1935, Serial No. 27,441

5 Claim.

This invention relates to a mirror and more particularly to a body provided with an improved metallic reflecting surface.

An object of the invention is to provide a mir ror or reflecting surface therefor which has new and important qualities with respect to reflection of the various light regions and also with respect to hardness, wear-resisting character, adaptability to cleaning, etc.

The invention is illustrated, in a preferred embodiment, by the accompanying drawing, in which is shown a broken perspective view of a mirror embodying my invention.

The mirror body may be formed of glass, metal, or any other suitable material. If desired, the entire mirror may be formed of an alloy hereinafter described as useful for providing a reflecting surface.

The reflecting surface is preferably formed of an alloy in which aluminum is combined with another metal, and more particularly magnesium.

Aluminum has been combined with various metals to produce reflecting surfaces. It has been combined with magnesium to form magnalium, and with magnesium and copper in forming duralumin. Aluminum has a coefficient of reflection of 89.5% in the visible spectrum. Magnalium has a coeflicient of 83.3 to 84.3% in the visible spectrum. Duralumin has a very low coefiicient-in the neighborhood of 53%. While pure aluminum has a higher coefiicient than the above alloys of aluminum and magnesium, it has the disadvantage of being relatively soft and non-resistant to wear. The addition of magnesium to aluminum to form the above alloys, while increasing the hardness of the product, very materially reduces the coeflicient of reflection.

I have discovered that magnesium may be combined with aluminum in such a way as to increase the hardness of the product, while at the same time increasing the coefficient of reflection of the product materially above that of pure aluminum. I have discovered that there are certain critical limits within which aluminum and magnesium maybe combined to produce a product of the abovementioned advantages. When the magnesium content of the alloy is increased from zero to 2 or 3%, the reflection coeflicient of the pure aluminum (89.5%) is increased to 94% and in some instances to 96%. When the magnesium content is increased to approximately 8%, the product has a uniformly high coeflicient of reflection.

Through this range, there is a change in the hardness of the product as will be later mentioned. When the magnesium content is increased substantially above 8%, there is a dropping off in the reflection coefficient, and when the content of .magnesium reaches 10%, the results are definitely inferior as far as the coefficient of reflection is concerned. In other words, as the amount of magnesium is increased beyond 8%, the reflection coefficient falls appreciably until it reaches a final value of about 82%, which is the reflection coemcient for pure magnesium. Furthermore, as the amount of magnesium ranges from 10% or great- 10 er, there is a definite bluish cast to the surface with a greater reduction in the reflection coeflicient at the red end of the spectrum.

As to the quality of hardness in the product, I

find that in the above range of from 98% alumi- 5 num and 2% magnesium to approximately 92% aluminum and 8% magnesium, the surface hardness of the product was approximately two and one-half to three times that of aluminum, and after the alloy was heat-treated under the well known methods employed for heat-treating aluminum-magnesium alloys, the hardness was found to be more than ten times that of the pure alu minum surface. The hardness of the product seemed to be greatest when the magnesium content was in the neighborhood of 5%. Such an alloy furnished a surface which, when tested, proved to be harder than a chromium surface. As the magnesium content was increased to 10% or more, I found that the hardness of the product was considerably less. Often such mirrors were spoiled by the mere attempt to remove fingermarks from them.

The mirror may be formed by any suitable method. It may be formed as a solid alloy body, or by depositing the alloy upon a body such as metal, glass, etc. If deposited upon glass, it may be deposited upon the front surface thereof or the rear surface. When freshly deposited upon a surface, the alloy oxidizes in contact with air to 40 form a surface consisting largely of an oxide of aluminum. During the first two or three weeks, the alloy crystallizes or ages, producing a hard basic structure, the surface oxide of which is exceedingly hard. Unlike silver, which combines 45 Surface contamination due to a de- 50 by any suitable method. One method, in which 55 thealloy-is'vaporized under reduced pressure and the vapor caused to condense upon the surface of the mirror body, is set out fully in my copending application Serial No. 666,805, for Mirrors and process of making same. It will be understood, however, that other suitable or well known methods for depositing alloys in liquid or vapor form upon a surface may be employed in forming my mirror product.

Under certain circumstances, I have found that antimony may be substituted for magnesium with beneficial results. For example, I have discovered that an alloy containing 10% antimony and 90% aluminum produces a mirror having a coefficient of reflection of 94%. The antimonyaluminum mirror has a beautiful clear white appearance very similar to that of the composition described above, but it is not quite as hard as the aluminum-magnesium product. Satisfactory results have been obtained with the antimonyaluminum alloy with the content of antimony varying between 3 and less than 30%. The product is harder than pure aluminum and has a coefficient of reflection well above that of aluminum.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible, in view of the prior art.

I claim:

1. A mirror having a surface consisting of aluminum and magnesium as the active optical constituents-said alloy of aluminum and magnesium being substantially unmixed with elements lowering the coefficient of reflection of said alloy, the proportions of aluminum and magnesium being between 98% aluminum and 2% magnesium on one side and 92% aluminum and 8% magnesium on the other.

2. A mirror comprising a mirror body having a reflecting surface sufiiciently uniform to reflect light substantially without diffusion, said surface consisting of aluminum and magnesium, the magnesium content of which is from 2 to 8% and the aluminum content of which is from 92 to 98%.

3. A mirror having a surface consisting of an aluminum-magnesium alloy, in which the magnesium and aluminum are the .active optical constituents, said alloy being unmixed with elements substantially lowering the coeificient of reflection of said alloy, the proportion of magnesium content being in the neighborhood of 5% and the proportion of aluminum content being in the neighborhood 'of 95%.

4. A mirror having a surface consisting of an alloy containing only aluminum and magnesium, the magnesium content of the alloy varying from substantially 2% to approximately 8%.

5. A mirror having a surface consisting of an alloy containing only aluminum and magnesium, the proportions of the magnesium content being in the neighborhood of 5%.

HIRAM W. EDWARDS. 

